ABSTRACT
Static and kinetic experiments on an accelerator-driven system have been conducted at the Kyoto University Critical Assembly. A small neutron detector using wavelength shifting fiber that can be inserted into a narrow space has been developed for measuring static and kinetic parameters. This study has found that the new detector type can be applied to kinetic experiments such as subcriticality measurements with the use of a D-T pulsed neutron source.
ABSTRACT
A small neutron detector using an optical fiber was previously developed for reaction rate measurements at research reactors and accelerator facilities. This detector can be inserted into narrow spaces and its spatial resolution is less than 1mm; however, its neutron sensitivity is low because of the small size of its detector. The purpose of this study is to develop a new optical fiber detector with high neutron sensitivity by using a wavelength shifting fiber. Through the measurement of the reaction rate distribution in a reactor core, we found that it is possible to increase the effective length of the detector, resulting in increased neutron sensitivity compared with a conventional optical fiber detector. Additionally, using a longer wavelength shifting fiber, the sensitivity can be increased until it is as large as that of a typical small BF(3) proportional counter, which means that this detector can be used for even low neutron flux fields.
ABSTRACT
To investigate the characteristics of a reactor and a neutron generator, a small scintillation detector with an optical fiber with ThO(2) has been developed to measure fast neutrons. However, experimental facilities where (232)Th can be used are limited by regulations, and S/N ratio is low because the background counts of this detector are increase by alpha decay of (232)Th. The purpose of this study is to develop a new optical fiber detector for measuring fast neutrons that does not use nuclear material such as (232)Th. From the measured and calculated results, the new optical fiber detector which uses ZnS(Ag) as a converter material together with a scintillator have the highest detection efficiency among several developed detectors. It is applied for the measurement of reaction rates generated from fast neutrons; furthermore, the absolute detection efficiency of this detector was obtained experimentally.
